The present invention relates to a functional semiconductor element for electrically and optically controlling signals which is indispensable to fast signal processing in the fields of switching and information processing.
It is now expected that wide-band, new services which utilize super wide band, ultrafast transmission, such as picture communication and video distribution, will become widespread. In this instance, ultrafast signal processing is indispensable at nodes to which wide-band signals concentrate. To meet this requirement, there has been called for capabilities in electrical or optical processing which permit a fast switching operation and further reduction of the processing time through parallel processing.
One of important functions in signal processing is a logic/arithmetic function. The implementation of such a function requires an electronic or optical device which performs and AND or OR operation as a logical operation which provides a different output signal, depending on whether all or any one of a plurality of bits is a "1" or not.
In FIG. 29 there is shown the band structure of an electronic device which performs an amplifying operation according to the prior art. Reference numeral 501 denotes an n-GaAs layer, 502 an i-GaAs layer, 503 a p-GaAs layer, 504 an i-GaAs layer, and 505 an n-GaAs layer. This device has what is called an n-i-p-i-n triangular barrier diode structure (TBD); the device is provided with source, gate and drain layers and is able to amplify a majority carrier flow by changing the voltage of an electrode mounted on the p-type gate layer. This device features a thin p-type gate layer, and hence permits a fast passage of carriers through the gate layer. FIG. 30 shows the gate voltage dependence of the current-voltage characteristic of this device. V.sub.G1 to V.sub.G4 denote gate voltages. Thus, this device is capable of performing the amplifying operation on the basis of the gate voltage and hence is promising in terms of fast operation, but its function is limited specifically to the amplifying operation as is the case with other transistors.
FIG. 31 shows the band structure of an optical device which performs an amplifying operation according to the prior art. Reference numeral 601 denotes an n-GaAs layer, 602 an i-GaAs layer, 603 a p-GaAs layer, 604 an i-AlGaAs layer, and 605 an n-AlGaAs layer. This device also has the so-called n-i-p-i-n triangular barrier diode structure (TBD) and is provided with source, gate and drain layers. By biasing and irradiating this device with light, minority carriers are generated in the drain layer and stored in the p-type layer to thereby change its potential, permitting the amplification of a majority carrier flow. This device also features a very thin gate layer, which allows carriers to pass therethrough at a high speed. In FIG. 32 there is shown the input-light power dependence of the current-voltage characteristic of this device. P.sub.1 to P.sub.3 denote the input-light power. This device is promising in terms of high-speed operation but has, as its function, only the amplifying operation as is the case with ordinary phototransistors.
In FIG. 33 there is shown a conventional XOR optical logic element. Reference numerals 700 and 700' denote phototransistors (HPT) each composed of an n-InP layer, a p-InGaAsP layer and an n-InP layer, and 701 and 701' LEDs each composed of an n-InP layer, In AsP layer and a p-InP layer. The LEDs are each connected in series to one of the two HPTs of the respective pairs which are simultaneously irradiated with input lightwaves A and B; two such units are connected in parallel to the power supply. FIG. 34 depicts the sectional structure of the unit cell surrounded by the one-dot chain line. Reference numeral 702 a semi-insulating InP layer, 703 an n-InP layer, 704 a p-InGaAsP layer, 705 an n-InP layer, 706 an InGaAsP layer, 707 a p-InP layer, 708 a p-InGaAsP layer, 709 an Au-Zu layer, 710 an Au-Sn layer, 711 a polyimide layer, and 712 a Ti/Au layer; the layers InGaAsP layers 704 and 706 correspond to the base layer of each HPT and the light emitting layer of each LED, respectively. When only the input light A (B; reference characters or numerals inside and output the parentheses correspond to each other in the following description) is incident on the device as shown in FIG. 34, the HPTs 700 (700') are tuned ON and the HPTs 700' (700) connected thereto are turned OFF, and consequently, only the LED 701 (701' ) emits light. On the other hand, when the input light A and B are simultaneously incident on the device, only the HPTs that are not connected to the LEDs 701 and 701' are turned ON, and consequently, neither of the LEDs 701 and 701' are supplied with current and emit light. When either the input light A or B are not incident, no current flows to anywhere, and hence no light is emitted. From these operations, it will be seen that the sums of the input light A and B and output light C and D from the LEDs just bear the exclusive-OR (XOR) relationship.
The electronic or optical device of such a conventional triangular barrier diode (TBD) type structure as described above does not possess a function of causing and stopping an avalanche multiplication. Hence, the device does not possess the function as an amplifying device which utilizes the avalanche multiplication; furthermore, it is equipped with a bistable or similar function through use of a feedback operation of another functional element part connected to the outside. This, however, introduces complexity in the device structure and lowers its response speed accordingly.